The present invention relates to a process for generating a low-voltage discharge, a process for igniting and operating the low-voltage discharge, a vacuum treatment apparatus with a treatment chamber, a cathode chamber for generating a low-voltage discharge and methods of using the apparatus.
It is known to use low-voltage arc discharges for various vacuum treatment processes. For example see Swiss Patent CHP 456,294 or CHP 551,497, and further CHP 645,137. Also see, "Ein Produktionsverfahren zur Herstellung dunner Schichten durch Kathodenzerstaubung im Hochvacuumbereich" {"A production process for the production of thin layers by cathode sputtering in the high-vacuum zone"}, Rudolf A. Lang Verlag, Wiesbaden, No. 7/66, pp. 161-164, or "Ein Verfahren zur Herstellung dunner Schichten durch Ionenzerstaubung im 10E-4 Toor Bereich" {"A process for the production of thin layers by ion sputtering in the 10E-4 Torrs range"}, F. P. Gaydou, Blazers Aktiengesellschaft, FL-Balzers, in reprints from Mikroelektronik 2, Oldenburg/MunchenVienna 1967, pp. 183-192. From these references, it is known to generating a low-voltage arc discharge in a vacuum treatment chamber, and to couple a cathode chamber via a diaphragm to the latter, with a thermionic cathode in the cathode chamber. The low-voltage arc discharge is customarily ignited with the aid of a separate ignition electrode which is placed at a positive anodic ignition potential with respect to the thermionic cathode.
After the ignition of the low-voltage discharge in the cathode chamber, the discharge is primarily maintained between the thermionic cathode and an anode disposed in the treatment chamber. The anode provided in the treatment chamber can be formed by at least part of the inner wall of the treatment chamber, or a separate anode arrangement can be disposed in the treatment chamber so as to be electrically insulated from the wall of the treatment chamber in such a way that the treatment chamber and the stated anode arrangement can be operated at a potential which is electrically separated. An anode arrangement of this type can be formed for example by a substrate carrier in the treatment chamber.
In particular apparatuses, such as are known for example from CHP 551,497, the diaphragm arrangement is operated electrically at floating potential, in other applications, such as are known for example from CHP 456,294, it is at the potential of the wall of the treatment chamber.
It has been found that in an arrangement of this type, arc discharges which are known under the term "arcing", develop in particular on portions of the inner wall of the treatment chamber, and specifically more strongly the more such portions are exposed to the discharge and the higher the electrical field strength is at such portions.
Arcing of this type places stress on the electrical feed apparatus which is provided for maintaining the discharge, and has other undesirable effects such as uncontrolled process behavior such as underbreaks and contamination, for example, through gas eruptions, sputtering-off or vaporization of materials not desired, etc. An implementation of the process can become entirely impossible under these conditions. A sputtering-off of the wall portions affected by the arcing in the case of delicate treatment processes in which an extremely pure and controlled treatment atmosphere is required, leads to intolerable contamination, for example.